1. Field of the Invention
The present invention relates to a multi-point teleconference system for performing a conference among a plurality of places using televisions, more particularly to a multi-point teleconference system which is effectively used in case where the number of the conference places is changed to two points to continue the teleconference on the way during the teleconference connecting more than two points.
2. Description of the Related Art
The multi-point teleconference system which is participated by persons existing in a plurality of places using televisions has become of major interest lately. This system is designed such that image data from each participant for the conference existing in different places is input by a television camera and voice information therefrom is input by a microphone (hereinafter referred to as mike), thereby outputting an image and voice of a speaker and the like from the television disposed in respective places.
FIG. 1 shows an example of such kind of the conventional multi-point teleconference system which is disclosed in Japanese Patent Application Laid Open Nos. 83407/93, 298146/92, and 327913/93, for example. In this multi-point teleconference system, teleconference terminal units 111.sub.1 to 111.sub.N arranged in respective places and a multi-point control unit 112 arranged in one place in the system are connected by means of an ISDN (Integrated Services Digital Network) public line 113.
In the foregoing structure of the conventional multi-point teleconference system, each of the teleconference terminal units 111.sub.1 to 111.sub.N comprises a television (not shown) which outputs an image and a voice, a television camera (not shown) which inputs an image, a microphone (not shown) which inputs a voice, and control processing section (not shown) which controls these input/output equipment. Moreover, the multi-point control unit 112 comprises a circuit which puts voice signals sent from each of the teleconference terminal units 111.sub.1 to 111.sub.N together to transmit the addition result to each of the teleconference terminal units 111.sub.1 to 111.sub.N, and a circuit which transmits a specified video signal among the video signals sent from each of the teleconference terminal units 111.sub.1 to 111.sub.N to them. For example, this circuit checks the voice signal sent from each of the teleconference terminal units 111.sub.1 to 111.sub.N and selects an image of the conference terminal unit exhibiting a level of the voice signal exceeding a reference value as the one of the speaking teleconference terminal unit, and transmits the selected image to each of the teleconference terminal units 111.sub.1 to 111.sub.N.
In such a multi-point teleconference system, each of the teleconference terminal units 111.sub.1 to 111.sub.N which participates in the conference sends an ISDN number of the multi-point control unit 112 to the ISDN public line 113 to make a connection thereto and performs the teleconferences therebetween. In this case, the multi-point teleconference is often scheduled to be carried out by connecting more than two places such as three places and five places. However, actually, in the case where a period of time of the conference is prolonged, a situation where a conference room used for that conference must be used for other conference may occur. Otherwise, a situation where some participants retire from the conference may also occur. These cases lead to a reduction in the number of the participants. As a result, carrying out of the teleconference by connecting two places is not rare.
In the foregoing multi-point teleconference system, there has been the following drawback. Specifically, even when the number of the places connected to the multi-point control unit 112 becomes two and the participants in the conference in these two places still continue it, participants in both places must pay connection fee of the line. This is because the fee for the time during the teleconference must be paid by the teleconference terminal unit on the sending side and both terminals have been connecting to the ISDN public line 113 by sending the ISDN number of the multi-point control unit 112. As a result, even when the number of the places where the participants exist becomes two, a cost will be twice as high as that at the case when the conference is performed simply by connecting two places so that an economical problem occurs. For this reason, at a time of point when the number of places where the participants become two, a method has been adopted, in which the teleconference is once interrupted and one teleconference terminal unit dials the ISDN number of the other teleconference terminal unit, thereby connecting both of the terminal units.
FIG. 2 is a flow chart showing switching control of line connections on the side of the multi-point control unit 112 of the conventional multi-point teleconference system. When the multi-point teleconference starts by a sending operation of a plurality of teleconference terminal units 111.sub.1 to 111.sub.N (step S101; Yes), at this point of time, the multi-point control unit 112 investigates the number of places which participate in the conference (step S102). The number of the places is found at this point of time by investigating how many times the teleconference terminal units 111.sub.1 to 111.sub.N have performed the line connection by sending the ISDN number to the multi-point control unit 112 for the conference. As a result of the investigation, when the teleconference terminal units 111.sub.1 to 111.sub.N more than two make the line connections to the multi-point control unit 112 (step S103; Yes), the teleconference by means of multi-point teleconference system starts (step S104).
Unless the participants in any places retire from the conference (step S105; No), the teleconference by the multi-point connections is continued (step S104). If retirement of the participants from the conference occurs (step S105; Yes), it is checked whether the number of remaining places where the participants exist is more than two (step S103). It is possible to investigate the present number of the participants in the conference based on the number of voice data collected from the teleconference terminal units 111.sub.1 to 111.sub.N to the multi-point control unit 112. When the present number of the participants in the conference is more than two (Yes), the step returns to S104 so that the teleconference by the multi-point connections is continued.
On the contrary, when the number of the places where the participants exist is reduced by any retirement to two (step S103; No), the participants in each place are allowed to confirm by looking at an image display whether switching to a point to point (referred to as P--P) connection is necessary (step S106). In the case where the multi-point teleconference is admitted since a person who retired from the conference is scheduled to return thereto or the conference is to be completed soon (step S107; No), the step returns to S104, so that the teleconference by the multi-point connections is continued.
On the other hand, when the switching to the P--P connection is required (Yes), the multi-point control unit 112 displays the ISDN number of the other station on the display for two places which are performing the conference for the present (step S108). The ISDN number of the other station may be informed only to one place which requires the switching to the P--P connection or only to the predetermined one place. Thereafter, the teleconference by the multi-point connection is completed and all of the lines connecting the participating places are disconnected (step S109).
Therefore, after that, the persons wishing to continue the teleconference perform sending operation of the ISDN number and connect the line between the finally remaining two places, whereby the teleconference by the P--P connection is performed. In the case of the teleconference by the multi-point connection, two participants of the conference on both sides are charged for payment. However, in the case of the teleconference by the P--P connection, the participant on one side will be charged for payment. As a result, the fee paid for the usage of the line will be reduced to a half in total.
In the conventional multi-point teleconference system, when the teleconference by the multi-point connection is switched to that by the two places connection, the lines must be once disconnected. Moreover, the remaining users must restart the teleconference by performing the P--P connection so that the procedure has been taken much time for the users; therefore, even when the multi-points where the teleconference is performed are reduced to two places, the teleconference by the multi-point connection tends to be continued. In this case, there has been a problem that the fee for the television connection by the multi-point connection is twice as high as the teleconference by the P--P connection because in the teleconference by the multi-point connection, the fee is charged for the participants on both sides. Moreover, when the teleconference by the multi-point connection is continued under these circumstances, the multi-point control unit 112 occupied by these two places during this period of time, resulting in a problem that other conferences can not be held with the multi-point control unit 112.